Like I said, there is an aspect of semantics involved here. Some conditions see both uses, like Alzheimer’s (example):
Alzheimer’s disease is a brain disorder that gets worse over time.
What is Alzheimer’s Disease?
- Alzheimer’s disease is the most common type of dementia.
- It is a progressive disease beginning with mild memory loss and possibly leading to loss of the ability to carry on a conversation and respond to the environment.
- Alzheimer’s disease involves parts of the brain that control thought, memory, and language.
It can seriously affect a person’s ability to carry out daily activities.
The dictionary definition of disease (Merriam-Webster) is compatible with the definition given above by Britannica:
a condition of the living animal or plant body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms
Oxford Learner’s Dictionary defines disease like this:
an illness affecting humans, animals or plants, often caused by infection
And Cambridge Dictionary:
illness of people, animals, plants, etc., caused by infection or a failure of health rather than by an accident
A disease is an illness which affects people, animals, or plants, for example one which is caused by bacteria or infection.
(note that microorganismal causes are mentioned as examples here, not as the only cause)
In other words, all the sources I’ve bothered to check include non-microorganismal causes for diseases. And it boils down to whether you want to argue against dictionaries or just go with the common use of words.